The present invention relates to an image reading apparatus and more particularly to an image reading apparatus incorporating a line light source for illumination of the image source.
An optical image reader or reading apparatus is conventionally constructed as an enclosed structure. Internal elements, such as a line light source, a rod lens and a light-receiving element, are enclosed in an internal space which is formed by a housing, a support plate and a window to the image source.
In many image scanning applications, the image source, such as a sheet of paper, is moved across the stationary platen of the image reader enclosure during scanning. In other image scanning applications, such as the use of hand-held scanners, the window of the enclosed image reader is manually moved across the stationary image source during scanning.
Image scanners have been developed, which employ charge coupled device (CCD) flat bed scanner technology that provides high image resolution. Using this technology, a line image having the length of a standard page is focused over a long focal length onto a remote image sensor or CCD sensor. Because of the long optical path, the image must be highly illuminated for sufficient resolution at the remote image sensor. Additionally, in order to make the long optical length more manageable, the optical path is typically xe2x80x9cfoldedxe2x80x9d within the system enclosure by way of optical configurations of mirrors and lenses.
It has been proposed to use an electric-discharge lamp such as a fluorescent lamp as a line light source for the image readers for low power consumption. A conventional fluorescent lamp includes a straight light emitting tube and two receptacles connected to the opposite ends of the light emitting tube, respectively. The light emitting tube may be divided into a middle section where luminescence is at a satisfactorily high level and two boundary sections where filaments are positioned and luminescence is low. The boundary sections define the opposite ends of the light emitting tube, respectively, and do not contribute to illumination of the image source. Thus, the middle section of the tube only contributes to illumination of the image source. The image reader is adapted to be moved in a first direction relative to the image source. The light emitting tube is elongated to extend across the window in a second direction that is orthogonal to the first direction. To highly illuminate the image at the edges of the window in the second direction, the middle section of the light emitting tube must be elongated to extend in the second direction with a length at least equal to a maximum extent of the window in the second direction. In this case, the boundary sections of the tube and the receptacles extend beyond the edges of the window in the second direction and a direction opposite to this second direction. A maximum extent of the housing of the image reader in the second direction is given after due consideration of not only the length of the middle section of the light emitting tube, but also the total length of the boundary sections and receptacles. Thus, a ratio of the maximum extent of the housing to the length of the middle section of the light emitting tube is not sufficiently small.
There remains a need for a compact image reading apparatus employing a fluorescent lamp as a line light source. More particularly, there remains a need for a fluorescent lamp appropriately constructed for making a great contribution to reduction of maximum extent of the housing in the second direction.
JP-A 58-123661 U proposes a fluorescent lamp to meet these needs to some extent. The fluorescent lamp according to this proposal has a straight fluorescent tube and two receptacles connected to the opposite ends of the tube. The receptacles have their projected electrodes elongated to extend in the first direction, while the tube and the receptacles are elongated to extend in the second direction. This fluorescent lamp has contributed to reduction of dimension in the second direction as compared to the case where the electrodes extend in the second direction and the opposite direction thereto. This reduction is not satisfactory, in amount, however.
An object of the present invention is to meet the above-mentioned needs at a satisfactorily high level.
According to one aspect of the invention, there is provided an image reading apparatus adapted to move in a first direction relative to a document, comprising:
a housing; and
a translucent lamp positioned within said housing as a line light source for illumination of a document,
said lamp having a light emitting tube, the light emitting tube including a middle section that is elongated in a second direction that is orthogonal to the first direction,
the light emitting tube including two boundary sections between which the middle section extends, the boundary sections having bent ends connected to the middle section at ends thereof, respectively,
the middle section and each of the boundary sections forming an angle, where the vertex of the angle is the adjacent bent end.
According to a specific aspect of the present invention, there is provided an image reading apparatus adapted to move in a first direction relative to a document, comprising:
a housing having a window that is elongated in a second direction that is orthogonal to the first direction;
a translucent lamp positioned within said housing as a line light source for illumination of a document through the window,
said lamp having a light emitting tube, the light emitting tube including a middle section that is elongated in the second direction with a length at least equal to the maximum extent of the window,
the light emitting tube including two boundary sections between which the middle section extends, the two boundary sections having bent ends connected to the middle section at ends thereof, respectively,
the middle section and each of the bent ends forming an angle that is not greater than 90 degrees, where the vertex of the angle is the adjacent bent end,
whereby a ratio of a maximum extent of said housing in the second direction to the maximum extent of the window is reduced.